Display and multi-layer printed circuit board with shared flexible substrate

ABSTRACT

An electronic device may be provided with a display and a multi-layer printed circuit. Integrated circuits and other components may be mounted to the multi-layer printed circuit. The display and multi-layer printed circuit may share a common layer formed from a flexible substrate. The flexible substrate may have portions that are integrated into the display and portions that are integrated into the multi-layer printed circuit board. The flexible substrate may contain patterned conductive traces that are used to route signals from components in the multi-layer printed circuit to display circuitry such as a display driver integrated circuit. An array of thin-film transistors may be used to control the emission of light from the display and may be formed on portions of the flexible substrate that are integrated into the display. The display may be a flexible display that includes an array of organic light-emitting diodes.

BACKGROUND

This relates generally to electronic devices, and more particularly, todisplays for electronic devices.

Electronic devices such as cellular telephones, computers, and mediaplayers are often provided with displays for displaying images to auser. In a typical display, an array of active image pixels iscontrolled by display driver circuitry using a pattern of orthogonalcontrol lines.

The active image pixels form a rectangular active area in the center ofthe display. The active region in the center of the display issurrounded by an inactive border region. The inactive border regionincludes space for fanning out control lines from a centralized locationat which a signal cable for the driver circuitry is attached. The signalcable may be a flexible printed circuit that is used to route signalsfrom a main logic board or other printed circuit board to the drivercircuitry. Typically, a conductive adhesive is used to mount one end ofthe signal cable to the display. A board-to-board connector is oftenused to connect the opposing end of the signal cable to a printedcircuit board.

Ensuring that there is sufficient area to reliably attach the signalcable and to fan out the control lines along the edges of the activearea may require a significant amount of inactive border area. It is notuncommon for the width of the inactive border to be up to a centimeterwide or more. This type of wide inactive region tends to make displaysbulky and requires the use of electronic device housings with widebezels. Connecting structures such as board-to-board connectors used toconnect the signal cable to the printed circuit board may also addundesirable bulk to an electronic device.

It would therefore be desirable to be able to provide improvedelectronic devices.

SUMMARY

Electronic devices may be provided with a display and a multi-layerprinted circuit. The multi-layer printed circuit board may be a flexibleprinted circuit, a rigid printed circuit board (PCB), or may have acombination of rigid and flexible layers (sometimes referred to as a“rigid-flex” printed circuit board). Integrated circuits and othercomponents may be mounted on the multi-layer printed circuit.

The display and the multi-layer PCB may be provided with a sharedflexible substrate layer. The flexible substrate may have a firstportion that forms a layer in the display and a second portion thatforms a layer in the multi-layer PCB. An array of thin-film transistorsmay be mounted on the first portion of the flexible substrate and may beused to control the emission of light from the display. Patternedconductive traces in the flexible substrate may be used to conveysignals from components and circuitry in the multi-layer PCB to displaycircuitry such as display driver circuitry.

Vertical conductive structures such as vias may be used to form anelectrical connection between layers in the multi-layer printed circuitand the second portion of the flexible substrate or between layers ofthe multi-layer printed circuit that are formed on opposing sides of thesecond portion of the flexible substrate.

In some configurations, the first portion of the flexible substrate mayform an integrated layer of the display and the second portion may beattached to a printed circuit using a connecting structure such as aboard-to-board connector. In other configurations, the first portion ofthe flexible substrate may be attached to the display using a conductivematerial (e.g., conductive adhesive, solder, etc.) and the secondportion may form an integrated layer of a printed circuit.

If desired, the flexible substrate layer may form an integrated layer ofa main logic board or other rigid logic board.

Further features of the invention, its nature and various advantageswill be more apparent from the accompanying drawings and the followingdetailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an illustrative electronic device suchas a handheld electronic device with a display in accordance with anembodiment of the present invention.

FIG. 2 is a cross-sectional side view of a portion of an illustrativeelectronic device having a shared flexible substrate layer that forms anintegrated layer of a display and a printed circuit board in accordancewith an embodiment of the present invention.

FIG. 3 is a cross-sectional side view of a portion of an illustrativeelectronic device having a flexible substrate layer that forms anintegrated layer of a printed circuit board in accordance with anembodiment of the present invention.

FIG. 4 is a cross-sectional side view of a portion of an illustrativeelectronic device having a flexible substrate layer that forms anintegrated layer of a display in accordance with an embodiment of thepresent invention.

FIG. 5 is a perspective view of a portion of an illustrative electronicdevice having a shared flexible substrate layer that forms an integratedlayer of a display and a printed circuit board in accordance with anembodiment of the present invention.

FIG. 6 is a perspective view of a portion of an illustrative electronicdevice having a shared flexible substrate layer that forms an integratedlayer of a display and a plurality of printed circuit boards inaccordance with an embodiment of the present invention.

FIG. 7 is a cross-sectional view of a portion of an illustrativeelectronic device having a shared flexible substrate layer that isbonded to layers in a printed circuit board using a conductive materialin accordance with an embodiment of the present invention.

FIG. 8 is a cross-sectional view of a portion of an illustrativeelectronic device having a shared flexible substrate layer and a printedcircuit board with vias that interconnect components and printed circuitboard layers in accordance with an embodiment of the present invention.

FIG. 9 is a cross-sectional perspective view of a portion of anillustrative electronic device having a shared flexible substrate layerthat forms an integrated layer of a display and is partially insertedinto a printed circuit board in accordance with an embodiment of thepresent invention.

FIG. 10 is a cross-sectional side view of a portion of an illustrativeelectronic device having a printed circuit board with heat sink layersin accordance with an embodiment of the present invention.

FIG. 11 is a cross-sectional side view of a portion of an illustrativeelectronic device having a printed circuit board with shielding layersin accordance with an embodiment of the present invention.

FIG. 12 is a cross-sectional side view of a portion of an illustrativeorganic light-emitting diode display having a shared flexible substratelayer in accordance with an embodiment of the present invention.

FIG. 13 is a cross-sectional side view of a portion of an illustrativeorganic light-emitting diode display in accordance with an embodiment ofthe present invention.

FIG. 14 is a top view of a portion of an illustrative electronic devicehaving a shared flexible substrate layer that is directly integratedinto a display and a main logic board in accordance with an embodimentof the present invention.

DETAILED DESCRIPTION

A display may be provided for an electronic device such as a portableelectronic device. Displays may be used to display visual informationsuch as text and images to users.

Displays may be coupled to circuitry within the electronic device suchas circuitry on a printed circuit board. For example, a display maycontain driver circuitry that receives image data, control signals orother signals from a printed circuit board in the device. A flexiblesubstrate layer may be used to convey image data and other signals fromthe printed circuit board to the driver circuitry in a display. Theflexible substrate layer may have one portion that is directlyintegrated into the display (e.g., the flexible substrate may form alayer in the display). The flexible substrate layer may have a secondportion that is directly integrated into the printed circuit board(e.g., the flexible substrate may form a layer in the printed circuitboard).

An illustrative electronic device of the type that may be provided witha flexible substrate layer that is directly integrated into a display, aprinted circuit board, or both the display and the printed circuitboard, is shown in FIG. 1. Electronic device 10 may be a portableelectronic device or other suitable electronic device. For example,electronic device 10 may be a laptop computer, a tablet computer, asomewhat smaller device such as a wrist-watch device, pendant device, orother wearable or miniature device, a cellular telephone, media player,electronic books, etc. The electronic device might be a larger device aswell, such as a television or digital sign.

Device 10 may include a housing such as housing 12. Housing 12, whichmay sometimes be referred to as a case, may be formed of plastic, glass,ceramics, fiber composites, metal (e.g., stainless steel, aluminum,etc.), other suitable materials, or a combination of these materials. Insome situations, parts of housing 12 may be formed from dielectric orother low-conductivity material. In other situations, housing 12 or atleast some of the structures that make up housing 12 may be formed frommetal elements.

Device 10 may include components such as buttons, input-output portconnectors, ports for removable media, sensors, microphones, speakers,status indicators, and other device components. As shown in FIG. 1, forexample, device 10 may include buttons such as menu button 16. Device 10may also include a speaker port such as speaker port 18 (e.g., to serveas an ear speaker for device 10).

Device 10 may include one or more displays such as display 14. Display14 may be rigid or flexible or may have a combination of rigid andflexible layers. For example, a flexible display may include a flexibledisplay layer (e.g., a flexible organic light-emitting diode array and athin-film transistor layer formed on a flexible substrate). For thepurpose of this invention, organic light-emitting diode displays areintended to encompass all types of light-emitting displays that comprisethin organic film layers, including displays comprising organic smallmolecules, polymers, dendrimers, and quantum dots. The thin film layerswithin the organic light emitting display may comprise a cathode layer,an anode layer, one or more emissive layers, one or more hole transportlayers, one or more electronic transport layers, capping layers, holeinjection layers, electron injection layers, exciton blocking layers,and blends and composites of these materials. Other types of flexibledisplay technologies may be used to form a flexible display (e.g.,electronic ink displays, electronic paper displays, flexible liquidcrystal displays, flexible electrochromic displays, flexibleelectrowetting displays, etc.).

As another example, a liquid crystal display (LCD) may include a layerof liquid crystal material sandwiched between a color filter layer and athin-film transistor layer. In general, display 14 may be based on anysuitable display technology (liquid crystals, light-emitting diodes,organic light-emitting diodes, plasma cells, electronic ink arrays,electronic paper displays, etc).

Display 14 may include touch-sensitive elements (i.e., display 14 may bea touch screen). The touch sensitive elements may include an acoustictouch sensor, a resistive touch sensor, a piezoelectric touch sensor, acapacitive touch sensor (e.g., a touch sensor based on an array ofindium tin oxide capacitor electrodes), a photosensitive touch sensor,or a touch sensor based on other touch technologies.

Display 14 may include a rectangular center portion (as indicated bydashed line 20 in FIG. 1) that includes an array of display pixels andis sometimes referred to as the active portion of display 14. Theperipheral outer portion of display 14 (i.e., rectangular peripheralring 22 of FIG. 1) may include circuitry that does not emit light andmay therefore be referred to as the inactive portion of display 14.

Display 14 may receive image data from a main logic board, other printedcircuit board, or other circuitry in the electronic device. Display 14may transmit signals (e.g., touch input from a user of device 10) to amain logic board, other printed circuit board or other circuitry. Forexample, display driver circuitry may be mounted on a display layer suchas a thin-film transistor (TFT) layer. The display driver circuitry mayreceive image data from a printed circuit board or return touch input toa printed circuit board. Control lines such as gate lines may be used todistribute signals to the display from the display driver circuitry.

In a conventional electronic device, a signal cable formed from aflexible printed circuit is used to convey image data from a printedcircuit board to the display driver circuitry. In a typical arrangement,a first end of the flexible printed circuit is electrically connected tothe TFT layer in a display. A layer of anisotropic conductive film isoften used to mount the first end of flexible printed circuit to the TFTlayer. A second end of the flexible printed circuit is electricallyconnected to a printed circuit board (PCB) in the device. Aboard-to-board connector is often used to connect the second end of theflexible printed circuit to the PCB.

A flexible printed circuit does not emit light and is thereforetypically mounted in the inactive portion of a display. This creates anundesirable amount of inactive display area around the border of adisplay.

Device 10 may be provided with a flexible substrate layer that includesconductive paths for conveying data signals from a printed circuit boardto the display or from the display to the printed circuit board. Theflexible substrate layer may have one or more portions that form a layerof the display. The flexible substrate layer may have one or moreportions that form a layer of the printed circuit board. The flexiblesubstrate layer may have some portions that form a layer of the displayand other portions that form a layer of the printed circuit board. As anexample, the flexible substrate layer may have opposing ends. One orboth of the opposing ends may be directly integrated into the displayand/or the printed circuit board.

A flexible substrate layer having some portions that form a layer of adisplay and/or some portions that form a layer of a printed circuitboard may reduce inactive display area and may reduce or eliminate theneed for connecting structures on the display and/or the printed circuitboard that add undesirable bulk to an electronic device.

A cross-sectional side view of an illustrative arrangement in which ashared flexible substrate forms an integrated layer of both a displayand a printed circuit board is shown in FIG. 2. As shown in FIG. 2,display 14 may have one or more display layers such as display layer14A. Display layer 14A may contain an array of active display pixels andmay therefore form the active portion of display 14. Display layer 14Amay be formed from glass, ceramic, plastic, flexible sheets of materialsuch as polymers (e.g., polyimide, polyethylene terephthalate, or othermaterials that are capable of being provided in thin flexible sheets),other suitable materials, or a combination of these materials.

Display layer 14A may include multiple layers such as a touch-sensitivelayer (e.g., a sheet of polymer with an array of transparent capacitorelectrodes for a capacitive touch sensor), optical layers such aspolarizing layers, shielding layers (e.g., for preventing electricfields from disrupting the operation of the display), heat sinkinglayers (e.g., for conducting heat away from the display), sealing layers(e.g., layers of sealant formed from thin films, polymers, inorganicmaterials, metal foils, composites, etc.), cover layers (e.g., a layerof cover glass), other suitable display layers, or a combination ofthese display layers.

Portions of a flexible substrate such as flexible substrate 24 may forma layer of display 14. For example, portion 24A of flexible substrate 24may form a display substrate for display 14. If desired, circuitry foroperating display 14 may be mounted on portion 24A of flexible substrate24. For example, an array of thin-film transistors may be formed on thesurface of flexible substrate 24 in region 24A and may be used tocontrol emission of light from display 14. Transistors that may beformed on portion 24A of substrate 24 include polycrystalline silicontransistors, amorphous silicon transistors, organic thin-filmtransistors, metal oxide transistors, carbon nanotube or graphenetransistors, other nanoparticle-based transistors, etc.

The transistors of the array may be controlled by control signals fromdriver circuitry such as display driver circuitry 26 (e.g., a driverintegrated circuit). Display driver circuitry 26 may, if desired, bemounted on flexible substrate layer 24 and may be used to supply controlsignals to the array of transistors. This is, however, merelyillustrative. If desired, driver circuitry 26 may be formed as anintegral portion of flexible substrate 24. If desired, circuitry such asthin-film transistors and display driver integrated circuits may beformed entirely within flexible substrate 24, between flexible substrate24 and display layer 14A, partially within display layer 14A, entirelywithin display layer 14A or partially within both display layer 14A andflexible substrate 24.

Portion 24B of flexible substrate 24 may form an integrated layer ofprinted circuit 30. Printed circuit 30 and other printed circuits indevice 10 may contain a stack of multiple layers such as layers 31. Forexample, a printed circuit may contain a combination of both rigid andflexible layers (sometimes referred to as a “rigid-flex” PCB). Amulti-layer printed circuit such as printed circuit 30 may sometimes bereferred to as a PCB stack or PCB stack-up. Layers 31 of PCB 30 may beformed from dielectrics such as fiberglass-filled epoxy (e.g., as arigid layer in a PCB stack) and polyimide (e.g., as a flexible layer ina PCB stack), FR-2 (phenolic cotton paper), FR-3 (cotton paper andepoxy), FR-4 (woven glass and epoxy), FR-5 (woven glass and epoxy), FR-6(matte glass and polyester), G-10 (woven glass and epoxy), CEM-1 (cottonpaper and epoxy), CEM-2 (cotton paper and epoxy), CEM-3 (woven glass andepoxy), CEM-4 (woven glass and epoxy), CEM-5 (woven glass andpolyester), paper impregnated with phenolic resin, polystyrene,polyimide, polytetrafluoroethylene (PTFE), plastic, other polymers,ceramics, or other suitable dielectrics.

Layers 31 may include attachment layers such as layers of prepreg (i.e.,pre-impregnated layers of fiber and resin). Layers of copper or otherconductive materials may be formed on the surfaces of layers 31. Forexample, one or more of layers 31 may have upper and lower surfaces thatare covered with a layer of metal such as copper.

Integrated circuits, discrete components such as resistors, capacitors,and inductors, and other electronic components 32 may be mounted to PCB30. Display driver circuitry 26 may receive image data from processingcircuitry in PCB 30 (e.g., from integrated circuits such as components32) and produce corresponding control signals for display 14. Flexiblesubstrate 24 may be used to route signals to display driver integratedcircuit 26 from components 32 or other circuitry in PCB 30. Flexiblesubstrate 24 may contain patterned conductive traces 102 (e.g.,conductive traces on flexible sheets of substrate such as polyimidesheets). Patterned conductive traces 102 may form signal lines thatconvey signals from PCB 30 (e.g., from integrated circuits such ascomponents 32) to display circuitry such as display driver circuitry 26.Driver circuitry 26 may distribute signals to the display pixels viatraces such as traces 17.

In the example of FIG. 2, portion 24A of flexible substrate 24 may forman integrated layer of display 14. Portion 24B of flexible substrate 24may form an integrated layer of PCB 30 (e.g., substrate 24 may form oneof the layer 31 in PCB stack 30). In configurations in which flexiblesubstrate 24 forms a portion of both display 14 and PCB 30, the need fora connecting structure such as a board-to-board connector to attachflexible substrate 24 to PCB 30 and the need for surface area formounting a separate structure to the display may be reduced oreliminated. Inactive borders around a display may therefore by reducedor eliminated. This arrangement may also simplify the interconnectsbetween display 14 and PCB 30 and thus reduce power consumption andincrease efficiency of the display.

If desired, portion 24A of flexible substrate 24 may be electricallycoupled to display 14 using a conductive material and the portion 24Bmay form an integrated layer of PCB 30, as shown in FIG. 3.

In the example of FIG. 3, display 14 may contain multiple layers such asdisplay layer 14A and display layer 14B. Display layer 14B may containcircuitry for operating display 14. For example, an array of thin-filmtransistors (TFTs) may be formed on the surface of display layer 14B andmay be used to control the emission of light from display 14.Transistors in layer 14B may include polycrystalline silicontransistors, amorphous silicon transistors, organic thin-filmtransistors, metal oxide transistors, carbon nanotube or graphenetransistors, other nanoparticle-based transistors, etc. The transistorsof the array may be controlled by control signals from driver circuitry26 (e.g., a driver integrated circuit). If desired, driver circuitry 26may be mounted on layer 14B.

Display layers 14A and 14B may be formed from glass, ceramic, plastic,flexible sheets of material such as polymers (e.g., polyimide,polyethylene terephthalate, or other materials that are capable of beingprovided in thin flexible sheets), other suitable materials, or acombination of these materials.

Flexible substrate 24 may be used to convey data signals between display14 and PCB 30. Portion 24B of flexible substrate 24 may form anintegrated layer of printed circuit 30. Data signals from circuitry inPCB 30 (e.g., data signals from processing circuitry or other componentssuch as components 32) may be routed to display layer 14B via patternedtraces 102 (sometimes referred to as signal lines) on flexible substrate24.

Portion 24A of flexible substrate 24 may be electrically coupled todisplay layer 14B. In the example of FIG. 3, conductive adhesive 38 andsolder pad 35 electrically couple conductive traces 102 on flexiblesubstrate 24 with conductive traces on display layer 14B such asconductive trace 33. Traces 33 may interconnect signal lines 102 fromflexible substrate 24 to display driver circuitry 26. Display drivercircuitry 26 may distribute signals to display 14 via conductive traces17.

If desired, portion 24B of flexible substrate 24 may be attached to PCB30 using a connecting structure and the portion 24A may form anintegrated layer of display 14, as shown in FIG. 4.

In the example of FIG. 4, portion 24B of flexible substrate layer 24 isconnected to PCB 30 using a connecting structure such as connectingstructure 34 (e.g., a board-to-board connector, zero insertion forceconnector, etc.).

Portion 24A of flexible substrate 24 may form an integrated layer ofdisplay 14. For example, portion 24A of flexible substrate 24 may form adisplay substrate for the display. If desired, circuitry for operatingdisplay 14 may be mounted on portion 24A of flexible substrate 24. Forexample, an array of thin-film transistors may be formed on the surfaceof flexible substrate 24 in region 24A and may be used to controlemission of light from display 14. Transistors that may be mounted onportion 24A of substrate 24 include polycrystalline silicon transistors,amorphous silicon transistors, organic thin-film transistors, etc.Display driver circuitry 26 may, if desired, be mounted on flexiblesubstrate layer 24 and may be used to supply control signals to thearray of transistors. This is, however, merely illustrative. If desired,driver circuitry 26 may be formed as an integral portion of flexiblesubstrate 24. If desired, circuitry such as thin-film transistors anddisplay driver integrated circuits may be formed entirely withinflexible substrate 24, between flexible substrate 24 and display layer14A, partially within display layer 14A, entirely within display layer14A or partially within both display layer 14A and flexible substrate24.

As described above in connection with FIGS. 2 and 3, patterned traces102 on flexible substrate layer 24 may be used to form signal lines thatconvey data signals between circuitry on PCB 30 and display circuitrysuch as display driver circuitry 26. Because flexible substrate layer 24forms an integrated layer of display 14, no surface area is required formounting a separate structure to the display. This may reduce the amountof inactive display area around the border of a display and allowsignals to be conveyed directly from traces on flexible substrate 24 todisplay driver circuitry 26. Simplifying the interconnects betweendisplay 14 and PCB 30 in this way may help reduce power consumption,increase efficiency, and improve reliability of the display.

Flexible substrate layer 24 may have some portions that form a layer ofdisplay 14 and some portions that form a layer of PCB 30 that protrudesfrom multiple edges (sides) of PCB 30 as shown in FIG. 5. In the exampleof FIG. 5, flexible substrate layer 24 protrudes from two edges (sides)of PCB 30. This is merely illustrative. Flexible substrate layer 24 mayprotrude from one side, from two sides, from three sides, or from allfour sides of PCB 30.

If desired, a flexible substrate layer such as flexible substrate layer24 may form a layer of one or more PCB stacks and/or one or moredisplays as shown in FIG. 6. In the example of FIG. 6, flexiblesubstrate layer 24 is integrated into a plurality of PBC stacks such asPCB stack 30A and PCB stack 30B. Some portions 24B′ of flexiblesubstrate layer 24 may form a layer of PCB stack 30A while otherportions 24B″ may form a layer of PCB stack 30B. Portion 24A of flexiblesubstrate layer 24 that is integrated into display 14 may containcircuitry such as circuitry for operating display 14. Signals may berouted between PCB 30A, PCB 30B, and display 14 via conductive traces102 in flexible substrate layer 24.

As shown in FIGS. 2, 5, and 6, a single flexible substrate such asflexible substrate 24 may have at least one portion that forms a layerin a multi-layer PCB and at least one portion that forms a layer in adisplay. Other configurations in which a shared flexible substrate layeris directly integrated into both a display and a PCB may be used. Theexamples shown in FIGS. 2, 5, and 6 are merely illustrative. If desired,flexible substrate 24 may be formed as an integral portion of a PCBstack-up. If desired, one or more PCB stack-ups may be prefabricated andmounted on opposing sides of flexible substrate 24 as shown in FIG. 6.

FIG. 7 is a side view of an illustrative configuration that may be usedto attach portion 24B of flexible substrate layer 24 to PCB stack 30. Alayer of conductive material such as conductive adhesive 44 may beinterposed between flexible substrate layer 24 and adjacent layers 31Aand 31B of PCB 30. Conductive adhesive 44 may be formed from anisotropicconductive film (ACF) or other suitable conductive adhesives that willform an electrical bond between contacts or conductive traces in PCB 30and contacts or conductive traces in flexible substrate layer 24.Adhesives, conductive foam, conductive springs, welds (e.g., laserwelds), solder joints, or other types of bonds may be used in connectingthe conductive and/or dielectric materials in flexible substrate layer24 and PCB 30. The use of conductive adhesive as shown in FIG. 7 ismerely illustrative.

If desired, layers 31 of PCB 30 may be electrically connected to otherlayers 31 through flexible substrate 24 as shown in FIG. 8. As shown inFIG. 8, vertical conductive structures such as conductive vias 46 may beused to electrically connect interconnects in different layers of PCB30. As shown in FIG. 8, vias 46 may be plated or hollowed vias that linevertical openings 39 in the PCB stack. If desired, other types of viasmay be used (e.g., vias may be filled or partially filled withconductive material).

Vias such as vias 46 may be contained entirely within the interior ofPCB 30 (sometimes referred to as buried vias), may connect an exteriorsurface of PCB 30 to an interior surface of PCB 30 (sometimes referredto as blind vias), or may pass through the entire thickness of PCB(sometimes referred to as through vias). Vias 46 may be formed usinglaser drilling, mechanical drilling (i.e., with a drill bit) or othermechanical machining techniques. Openings 39 may be filled or coatedusing metal (e.g., copper) plating techniques, by filling openings 39with conductive paste, by filling openings 39 with conductive adhesive,or by filling openings 39 with other conductive material. Materials thatmay be used in forming vias 46 include copper, silver, gold,copper-tungsten, other suitable metals, carbon-based or organicconductors, or a combination of these materials. Other methods orstructures may be used to electrically connect different layers of PCBstack 30 that includes shared flexible substrate layer 24. The use ofconductive vias 46 as shown in FIG. 8 is merely illustrative.

If desired, the flexible substrate layer may form a partial layer of aPCB stack as shown in FIG. 9. For example, flexible substrate layer 24may only be partially inserted into the stack of PCB layers. In theexample of FIG. 9, a portion such as portion 30-1 of PCB stack 30includes layers 31 on opposing sides of a portion of flexible substratelayer 24. Flexible substrate 24 may therefore be integrated as a layerof portion 30-1 of PCB stack 30. Flexible substrate layer 24 may not beincluded in a portion of the PCB such as portion 30-2 of PCB 30.

Layers 31 of PCB stack 30 may have conductive layers such as conductivePCB layers 30C and dielectric layers such as dielectric PCB layers 30D.Conductive layers 30C may be patterned metal layers for forminginterconnects. Dielectric layers 30D may be alternating layers ofprepreg and core material (e.g., FR-4) or other suitable dielectriclayers. Electrical contacts such as contacts 21 may be used to connecttraces 102 on flexible substrate layer 24 with traces in PCB stack 30.Electrical contacts in PCB 30 such as contacts 21 may be contact pads,solder pads, or interconnect structures, or may be formed from patternedconductive layers in PCB 30 (e.g. layers such as PCB layers 30C), orother suitable conductive structures. Contacts 21 may, for example, beformed from copper or copper plated with gold or other materials.Contacts 21 may be electrically connected to the interconnects of PCB 30(e.g., using vias such as vertical vias 46 of FIG. 8, using parts ofhorizontal interconnects in layers 30C, etc.).

Components such as components 32 may be mounted on PCB 30. Components 32or other circuitry associated with PCB 30 may generate heat that maydamage components 32 or PCB 30. PCB 30 may be provided with heat sinkstructures such as heat sink layer 31H of FIG. 10. As shown in FIG. 10PCB stack 30 may include a heat sink structure such as heat sink layer31H that is formed over shared substrate layer 24. Heat sink layer 31Hmay help dissipate heat that is generated by components in PCB stack 30.Heat sink layer 31H may also help conduct heat away from display 14.

If desired, PCB 30 may be provided with one or more shielding layers asshown in FIG. 11. High frequency signals may be communicated betweendisplay 14 and PCB 30 during operation of display 14. Shielding layerssuch as shielding layers 31S may help block emission from these highfrequency signals that may cause electromagnetic interference (EMI) withcircuitry in PCB 30 or other components of device 10. Shielding layers31S may also reduce the amount of unwanted electromagnetic energyradiated by device 10. Shielding layers 31S may shield separate circuitsin PCB 30 from interfering with each other. Shielding layers 31S may beinterposed between substrate layer 24 and adjacent PCB layers 31A and31B. This is merely illustrative. PCB 30 may be provided with oneshielding layer, two shielding layers, three shielding layers, or morethan three shielding layers. Shielding layers such as shielding layers31S may be formed on one side of substrate 24 or on opposing sides ofsubstrate 24. If desired, PCB 30 may be provided without any shieldinglayers.

If desired, display 14 may be a flexible display that uses flexibledisplay technology such as an organic-light emitting diode (OLED) pixelarray formed on a flexible substrate. As shown in FIG. 12, display layer14A may include multiple layers formed on flexible substrate layer 24.Display layer 14A may include a circuitry layer such as thin-filmtransistor (TFT) circuitry layer 14-3 that includes an array ofthin-film transistors. Layer 14-3 may be formed on shared substratelayer 24, may be formed as a separate circuitry layer, or may haveportions formed in substrate layer 24 and portions formed in displaylayer 14A. TFT circuitry layer 14-3 may contain circuitry such asdisplay driver integrated circuits, gate line drivers formed fromlow-temperature polysilicon transistors, transistors formed fromamorphous silicon, metal oxide transistors, carbon nanotube or graphenetransistors, other nanoparticle-based transistors, etc. Circuitry andelectronic components in TFT circuitry layer 14-3 may be mounted onflexible substrate layer 24.

Display layer 14A may include a layer of light-emitting material such aslight-emitting layer 14-2. Light-emitting layer 14-2 may be formed overTFT circuitry layer 14-3. Light-emitting layer 14-2 may be formed froman array of organic-light emitting diodes (OLEDs) or otherlight-emitting material, such as quantum dots. If desired, OLED material14-2 may be formed from a thin film that is deposited or integrated intoTFT layer 14-1.

OLED layer 14-2 may be covered with a sealant such as sealant layer14-1. Sealant 14-1 may be formed from polymers (e.g., a layer of polymerthat is deposited over OLED layer 14-2), metal foil (e.g., a layer ofmetal foil that is laminated, sputtered, evaporated, or otherwiseapplied onto OLED layer 14-2), or other suitable coating or conformalcovering. If desired, sealant 14-1 may be formed from multiple layers.As shown in FIG. 13, sealant 14-1 may be formed from alternating layersof polymer 17 and inorganic material 19.

A shared flexible substrate layer that forms a layer of a display and amulti-layer PCB may also help directly connect a high density ofconductive traces in a PCB such as a main logic board to a low densityof conductive traces in a flexible substrate as shown in FIG. 14.

In the example of FIG. 14, main logic board 30 includes components suchas components 32. Components 32 may include integrated circuits such asa microprocessor, a microcontroller, an audio chip, anapplication-specific integrated circuit, or other integrated circuit. Ifdesired, discrete electrical components (e.g., resistors, inductors,capacitors, and transistors) may be mounted in internal cavities inprinted circuit board 30 or multiple integrated circuits may be mountedin internal cavities in printed circuit board 30. If desired, differenttypes of stand-alone components may also be embedded in printed circuitboard 30, such as antennas, sensors, power sources such as batteries andsupercapacitors, etc. The example of FIG. 14 is merely illustrative.

Some portions of flexible substrate layer 24 may form a layer in mainlogic board 30. Other portions of flexible substrate layer 24 may form alayer in display 14. Substrate 24 may contain patterned conductivetraces such as traces 102 that convey data signals from components 32 onboard 30 to display circuitry in display 14 (e.g., a driver integratedcircuit).

Traces on board 30 such as conductive traces 104 may be used todistribute data signals to signal lines 102 in substrate layer 24.Signals may travel from components 32 on the outermost layers of board30 to substrate layer 24 using vertical conductive structures such asconductive vias 46. Conductive traces 104 in board 30 may have arelatively high pitch (e.g., a high density of conductive traces)compared to signal lines 102 in substrate layer 24, which may have arelatively low pitch. Signal lines 102 may be form a pattern that fanshigh pitch traces 104 out from region 106 to low pitch traces 102 ofsubstrate 24.

Because shared substrate layer 24 forms an integrated layer in display14, signals from traces 102 may be routed directly to display circuitrywithout requiring any mounting surface area on display 14. Becauseshared substrate layer 24 forms an integrated layer in board 30, theneed for a connecting structure such as a board-to-board connector maybe eliminated. By simplifying interconnects between board 30 and display14, device 10 may be more efficient, may consume less power, may be morereliable, and may enable desirable design features.

The foregoing is merely illustrative of the principles of this inventionand various modifications can be made by those skilled in the artwithout departing from the scope and spirit of the invention.

What is claimed is:
 1. An electronic device, comprising: a displayhaving an array of display pixels; a printed circuit having a substrate;and a flexible substrate having a first portion that forms a layer inthe display, a second portion that is attached to the printed circuit,and a bent portion interposed between the first and second portions,wherein the array of display pixels is disposed on the first portion ofthe flexible substrate.
 2. The electronic device defined in claim 1wherein the display comprises an array of thin-film transistors formedon the first portion of the flexible substrate and wherein the array ofthin-film transistors is configured to control emission of light fromthe display.
 3. The electronic device defined in claim 2 wherein thedisplay further comprises a layer of organic light-emitting diodesformed over the array of thin-film transistors.
 4. The electronic devicedefined in claim 1 further comprising at least one integrated circuitmounted to the printed circuit.
 5. The electronic device defined inclaim 4 wherein the flexible substrate contains signal lines that conveysignals from the at least one integrated circuit to the display.
 6. Theelectronic device defined in claim 1 wherein the second portion of theflexible substrate is attached to the printed circuit using aboard-to-board connector.
 7. An electronic device, comprising: a printedcircuit having a substrate; and a display having a flexible substrate,wherein the flexible substrate comprises a first portion on which anarray of display pixels are formed, a second portion that is connectedto the printed circuit, and a bend between the first portion and thesecond portion.
 8. The electronic device defined in claim 7 wherein thearray of display pixels comprises an array of organic light-emittingdiode display pixels.
 9. The electronic device defined in claim 7wherein the flexible substrate comprises polyimide.
 10. The electronicdevice defined in claim 7 further comprising at least one integratedcircuit mounted to the printed circuit.
 11. The electronic devicedefined in claim 10 wherein the flexible substrate includes signal linesthat convey signals from the at least one integrated circuit to thearray of display pixels.
 12. The electronic device defined in claim 7wherein the first portion of the flexible substrate overlaps the secondportion of the flexible substrate.
 13. The electronic device defined inclaim 7 wherein the array of display pixels comprises thin-filmtransistor circuitry formed on the first portion of the flexiblesubstrate.
 14. The electronic device defined in claim 13 wherein thearray of display pixels comprises light-emitting material formed overthe thin-film transistor circuitry.
 15. The electronic device defined inclaim 14 wherein the display comprises a layer of sealant formed overthe light-emitting material.
 16. The electronic device defined in claim7 wherein the printed circuit comprises a rigid printed circuit board.17. The electronic device defined in claim 7 wherein the printed circuitcomprises a flexible printed circuit.